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Protein needs are easily met among plant-based eaters

New research led by Doctors For Nutrition’s lead dietitian for NSW, Joel Craddock (APD) of the University of Sydney, highlights protein quality of plant-based dietary patterns, and points to limitations in the commonly-used Digestible Indispensable Amino Acid Score, or ‘DIAAS’.

In recent years, plant-based dietary patterns have been increasing in popularity, with a growing body of literature demonstrating significant associated health benefits, and for athletes, significant improvements in recovery and performance.

Protein intake is often raised as a macronutrient of concern for people following plant-based dietary patterns, particularly athletes; however there is no evidence that, with a wide variety of food intake required, intakes are not achieved easily.

Now, a new review has revealed limitations with the current Food and Agriculture Organisation-endorsed method for determining protein digestibility, the Digestible Indispensable Amino Acid Score (DIAAS).


The DIAAS was principally designed for use in developing nations where protein intake and availability is scarce, however is now often used in Western nations. Emphasising protein quality in the West is typically unproductive, detracting from other truly prevalent nutritional shortcomings (such as fibre). Many of the limitations of the DIAAS are emphasised when used in groups following plant-based dietary patterns.

       Protein digestibility among plant-based eaters is underestimated by the current DIAAS methodology.

The DIAAS limits the contribution to overall dietary protein intake made by fruits, vegetables, meat analogs, nuts and seeds. This can be quite significant given those following plant-based dietary patterns consume a much greater quantity when compared to omnivores. This difference can mean true protein digestibility is underestimated.

In addition, assessment of protein digestibility is often made using single, uncooked protein isolates, whereas actual food is consumed cooked and with a variety of components, likely considerably increasing amino acid absorption.

Another more generalised point the research team flags is that the DIAAS has been modelled in animals such as pigs and rats. There are similarities in digestion between these animals and humans, but there are also substantial differences. Protein in these fast-growing animals is generally required for tissue growth, whereas in humans it’s largely required for maintenance.

These factors should be taken into account when assessing protein quality of overall plant-based dietary patterns, especially in individuals where a higher protein intake is recommended, such as in the case of athletes.

The review, published in Current Nutrition Reports in January 2021, is available online at SpringerLink.

Craddock, J.C., Genoni, A., Strutt, E.F. et al. Limitations with the Digestible Indispensable Amino Acid Score (DIAAS) with Special Attention to Plant-Based Diets: a Review. Curr Nutr Rep (2021).

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